# Picking the right subset of parameters

> A tool the agent can call without guessing needs a smaller parameter list. More than 8 top-level input properties is one place Toolcard looks.

Page date 2026-10-18. Rules version `2026-10-17.1`. The HTML page, which includes the same checker, is [here](https://agentghostedme.com/picking-the-right-subset-of-parameters.html).

On 2026-10-13, [@AvinashDalvi_](https://x.com/AvinashDalvi_/status/2110042506901786873) described the work as "translating it into something an agent could call without guessing, picking the right subset of parameters." Toolcard recorded that sentence on 2026-10-17. It is the only verbatim quote Toolcard uses from the post.

Toolcard's own summary of the note, already on the homepage, is that the work includes choosing which parameters to expose. The post states no number. 8 is Toolcard's cutoff. Nested properties are not counted.

These checks count keys on `inputSchema.properties`. They do not see which parameters a caller actually needed. An empty `findings` list means these checks did not fire. It does not mean the subset is the right one, and it does not mean the tool is good.

## What the wide-input check flags

Finding `wide-input` fires when `inputSchema` is a JSON object, its `type` is `object`, and `properties` has more than 8 keys. 8 keys do not fire it. A missing `properties` key is counted as zero. A name listed only in `required` is not counted. Nested keys under one property are not top-level keys.

Omitting `inputSchema` returns `missing-input-schema`, not `wide-input`. An `inputSchema` whose `type` is `string` returns `input-schema-not-object`, not `wide-input`. Those two checks follow the [MCP schema reference, 2025-06-18 revision](https://modelcontextprotocol.io/specification/2025-06-18/schema), which lists `inputSchema` as a required object schema.

The name and description checks are separate. Every row below uses the name `find_bill` and the description "Return the invoice that matches the number printed on the form." That description is 63 characters, so the description checks stay quiet. `find_bill` is not endpoint-shaped. The name check is explained on [MCP tools mapped 1:1 onto a REST API](https://agentghostedme.com/mcp-tools-mapped-1-to-1-onto-a-rest-api.md). The description checks are explained on [MCP server loads but the agent never calls the tool](https://agentghostedme.com/mcp-server-loads-but-the-agent-never-calls-it.md).

This table is `POST /v1/check` on this server on 2026-10-18. `stored` was false on each row. Rules version `2026-10-17.1`. The eight properties, in order, are `number`, `customer`, `status`, `issued_after`, `issued_before`, `currency`, `minimum_amount`, and `maximum_amount`. The ninth is `due_after`. The tenth is `due_before`. The nine nested keys are `name`, `email`, `id`, `city`, `region`, `postal_code`, `country`, `phone`, and `tax_id`.

| Top-level properties | Schema | Finding ids |
| --- | --- | --- |
| 0 | `properties` is `{}` | none |
| 0 | `type` is `object`, and `properties` is omitted | none |
| 1 | `number` | none |
| 1 | `customer` only, with the nine nested keys | none |
| 8 | the eight string properties | none |
| 8 | the eight, and `customer` has the nine nested keys | none |
| 8 | the eight, and `required` also names `due_after` | none |
| 9 | the eight plus `due_after` | `wide-input` |
| 10 | the nine plus `due_before` | `wide-input` |
| not sent | no `inputSchema` field | `missing-input-schema` |
| not counted | `inputSchema.type` is `string` | `input-schema-not-object` |

The 9-property row returns `wide-input` only. The 8-property row returns `findings: []`. Eight can still be the wrong subset. Toolcard does not treat that result as approval.

## Check

`find_bill` with those nine string properties returns `shape: not-endpoint-shaped` and finding id `wide-input`. `stored` is false.

```
curl -s -X POST https://agentghostedme.com/v1/check \
  -H 'content-type: application/json' \
  -d '{"name":"find_bill","description":"Return the invoice that matches the number printed on the form.","inputSchema":{"type":"object","properties":{"number":{"type":"string"},"customer":{"type":"string"},"status":{"type":"string"},"issued_after":{"type":"string"},"issued_before":{"type":"string"},"currency":{"type":"string"},"minimum_amount":{"type":"string"},"maximum_amount":{"type":"string"},"due_after":{"type":"string"}}}}'
```

`find_bill` with the same description and the eight string properties returns `shape: not-endpoint-shaped` and `findings: []`. Toolcard does not treat that result as approval.

Whether an agent later called the tool is a separate report. `POST /v1/outcomes` stores the name, a SHA-256 of the description if you sent one, and `called` or `ignored`. The [public summary](https://agentghostedme.com/v1/outcomes/summary) is counts only.

Rule list: [GET /v1/rules](https://agentghostedme.com/v1/rules). Home: [Toolcard](https://agentghostedme.com/).

Toolcard is not affiliated with the people or the projects cited.

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